To say the spending review is a little complicated is a bit of an
understatement, so here are some basics about the crux of why it's being
done: our national debt.

It is the money the Government has borrowed to buy or build things for the country, most of which goes back decades.

How big is it?

About £962billion. Which doesn't mean a lot to most people until you start to compare it to other big numbers: it's like winning the recent £113m Euromillions rollover jackpot every Friday for the next 13 years. Total debt is now higher than it has ever been.

To put it into more context, at the end of September, Britain's national debt was equivalent to about 64% of GDP, which is the total value of everything produced in the country. So, if it were possible, we could pay off the debt by every person and every business giving everything they earn from January 1 to the start of September to the Government. Simple.

A big chunk of the money we've borrowed has come from abroad. Just over a third of our total debt is owed to foreign investors. However, by far the biggest portion of our debt is owed to British institutions, including banks, pension funds, insurance companies and hedge funds. Individual investors are also owed a sliver of the pie.

Anyone can lend the Government money, which is, in effect, buying a bit of the national debt. The system is operated by the sale of gilts: you buy a gilt; the Government gets its extra cash; you get your money back plus a bit extra guaranteed at some point in the future. No gilt has ever failed to be repaid, which is why it's seen as such a safe investment, although the amount you earn is less than with riskier investments.

How does it compare to others?

The European Commission predicted in May that Britain's finances would be worse than any other major European country by the end of this year. However, this was before the Tories' emergency budget, so things may be getting better.

Spain and Ireland borrow less than Britain. Greece, however, is far worse than the UK, and is borrowing far more than its total GDP for the year.

China's national debt has been estimated at £1,048billion, although the official figure is much lower.

The US national debt now stands at well over £8,664billion, yes billion.

Why is it a problem?

The interest repayments on Britain's debt are simply huge. Currently, it's £120m a day. So that eats into the budget for everything else but we don't get anything to show for it. In the same way that credit card repayments stop you saving for a holiday, Britain's debt repayments are holding back investment in the country.

Another factor is whether those people wanting to buy the gilts I mentioned earlier believe they will definitely get their money back. This is called investor confidence and it's measured, among other things, by the ratings of agencies that specialise in such advice, such as Fitch, Moody's and Standard & Poor. The highest rating is AAA, which Britain currently has but that was under threat before the emergency budget.